Re: [PATCH v5 28/36] mm: add NODE_PRIVATE_CAP_HOTUNPLUG for opted-in private nodes

Gregory Price <[email protected]> Wed, 22 Jul 2026 10:04:49 -0400

Newsgroups	org.kernel.vger.linux-debuggers,dev.linux.lists.damon,dev.linux.lists.driver-core,dev.linux.lists.nvdimm,org.kernel.vger.cgroups,org.kernel.vger.kvm,org.kernel.vger.linux-cxl,org.kernel.vger.linux-doc,org.kernel.vger.linux-fsdevel,org.kernel.vger.linux-kernel,org.kernel.vger.linux-kselftest,org.kvack.linux-mm
Message-ID	<amDNMmbdE_ZhUgl1@gourry-fedora-PF4VCD3F>

On Mon, Jul 20, 2026 at 03:34:22PM -0400, Gregory Price wrote:
> Add CAP_HOTUNPLUG, which allows memory_hotplug to migrate a private
> node's folios for the purpose of hotunplugging memory.
> 
> Without this, hotunplug fails if any folio on the node is allocated.
> 
> Add node_allows_hotunplug() - which returns true for any normal node
> and private nodes with CAP_HOTUNPLUG.
> 
> Signed-off-by: Gregory Price <[email protected]>

after this question:
https://lore.kernel.org/linux-mm/al-pkvmgIxGu3LzM@gourry-fedora-PF4VCD3F/T/#m5b8166212a276fece2380f2dd03d6864375a576b

and some off-list feedback about limiting initial cap bits to active
use cases, I realized that this CAP bit can be entirely eliminated.

hotplug notifier callbacks already allow a driver to prevent memory
block state transitions - so that control already exists.

v6 will remove both the filtering here and the cap bit.

~Gregory